Field of the Invention
The present invention relates to a power supply apparatus, which is suitable for controlling a thermal fixing device mounted in an image forming apparatus such as an electrophotographic copying machine or a printer.
Description of the Related Art
In an image forming apparatus such as an electrophotographic copying machine or a printer, there is provided a fixing device configured to heat and fix an unfixed toner image onto a recording material to fix the unfixed toner image on the recording material. In a power supply apparatus configured to control supply of power to the fixing device, there has been widely used a method of subjecting AC voltage, which is supplied from an AC power supply, to a phase control using a bidirectional thyristor (hereinafter referred to as “triac”) or the like. As related arts associated with major functions of the above-mentioned power supply apparatus, the following technologies have been proposed. For example, in Japanese Patent Application Laid-Open No. 2007-212503, there is proposed a technology of detecting a current effective value of current which flows to the fixing device, to thereby detect power supplied to the fixing device. Further, for example, in Japanese Patent Application Laid-Open No. 2013-123348, there is proposed, in regard to a reference timing (hereinafter referred to as “zero cross”) during a phase control for power supplied from an AC power supply, a technology of detecting an accurate zero cross of the AC power supply while reducing power consumption of a circuit for detecting a zero cross. Yet further, for example, in Japanese Patent No. 4446136, there is proposed a technology associated with a discharging technology for an across-the-line capacitor (hereinafter referred to as “X-capacitor”) arranged between two lines of an AC power supply. Specifically, in Japanese Patent No. 4446136, there is disclosed a technology of detecting a state in which a power supply cable is drawn out from the AC power supply and discharging an electric charge charged in the X-capacitor, to thereby reduce power consumption during a normal time of a power supply apparatus.
With regard to the power supply apparatus configured to control supply of power to the fixing device, there has been a demand for reduction of power consumption at low cost. Therefore, there has been a problem of achieving the above-mentioned three functions including detection of the amount of power supplied to the fixing device, detection of the accurate zero cross of the AC power supply, and discharge of the electric charge charged in the X-capacitor, with a small-scale circuit configuration.